1. Field of the Invention
The present invention relates to a method and an apparatus for making semiconductor devices, especially for epitaxially growing several layers of crystal for use in semiconductor devices.
2. Description of the Prior Art
In recent years, technology of information conveyance is making a great progress, and above all, the art of light communication, which can transmit a large quantity of information with accuracy, attracts attention, and many experiments for actual use are now under way. Semiconductor lasers or light emitting diodes to be used in such light communication, should have a life of at least 10.sup.6 hours, since they are to be installed, for example, in long distance ocean light guide cables. In order to obtain such long life of the semiconductor devices such as lasers or light emitting diodes, it is very important to eliminate crystal imperfections of epitaxially grown crystal layers, especially those of the active region.
FIG. 1(a) shows a schematic sectional elevation view of a conventional apparatus used in making the semiconductor devices. The apparatus has a block 2 made of pure carbon, which holds a semiconductor substrate 1 in a recess on the principal (top) face thereof. A solution container 4 having a predetermined number of holes, which contains molten solutions 3 of semiconductor compounds or semiconductor mixed crystals, is slidably disposed on the upper face of the block 2. The apparatus of FIG. 1(a) is used in a manner that, at first the whole apparatus with material of the solution is heated to a predetermined temperature above the melting points of the solutions 3, and then the whole system is slowly cooled down at a predetermined cooling rate, and during the cooling down the solution container 4 is stepwisely slid towards the left side, thereby making the solutions 3 in the holes contact one by one to the principal surface of the substrate 1. Such type of the apparatus has the shortcomings that:
(1) since the depths, and hence quantities of the solutions which contact the substrate can not be accurately controlled by means of the structure of the apparatus, an accurate control of the epitaxially grown layers are difficult,
(2) since non-solved lumps exist in the solution, accurate controlling of quantity of the solution is impossible, and
(3) at sliding of the solution container 4, the surfaces of the epitaxially grown layers are undesirably scratched by edges of the solution holder 4 and the non-solved lumps, thereby damaging accuracy of the construction of the layers.
FIG. 1(b) shows a schematic sectional elevation view of another conventional apparatus used in making the semiconductor devices. The apparatus has a block 2' made of pure carbon, which holds a semiconductor substrate 1 in a recess on the principal face thereof. An overrider 9 which is also made of pure carbon is fixedly secured on the block 2'. The overrider 9 has a V-shaped bent hole, in the bottom of which the substrate 1 is disposed. A space 7 is connected to one end of a V-shaped bent hole 8 and has an opening 71 on the top thereof. The other end of the V-shaped hole 8 is made open to a waste solution depository. A piston 6 is provided in the opposite side in the space 7 to the V-shaped bent hole 8. A solution container 4 having a predetermined number of holes, and containing molten solutions 3 of semiconductor compounds or semiconductor mixed crystals, is slidably disposed on the upper face 91 of the overrider 9.
The apparatus of FIG. 1(b) is used as follows: At first, the whole system, and hence the solutions 3 are heated to a predetermined temperature, which is above the melting temperature of the solutions, and the solution container 4 is slid leftwards to such a position as to allow a first solution (in the leftmost hole) to be put into the space 7. Then the solution container 4 is slid again leftwards to such a position as to allow the bottom of a first isolation wall 41 between the solution containing holes to cover and seal the opening 71 of the space 7. Thereafter, the piston 6 is pushed leftwards, so that the first solution sealed in the space 7 is pushed leftwards into the V-shaped bent hole 8 and contacts the principal face of the semiconductor substrate 1, thereby making an epitaxial growth reaction to form an epitaxial layer of a predetermined thickness. Next, the piston 6 is pushed back rightwards and the solution container 4 is slid leftwards to such a position as to allow a second solution to be put into the space 7. Then the solution container 4 is slid again leftwards to such a position as to allow the bottom of the second isolation wall 42 to cover and seal the opening 71 of the space 7. Thereafter, the piston 6 is pushed leftwards, so that the second solution sealed in the space 7 is pushed down into the V-shaped hole 8, and hence pushes out the first solution which has been therein. By repeating the similar steps, all the solutions are made in contact with the face of the substrate 1 thereby making sequential epitaxial growths. Such type of the apparatus has the shortcomings that:
(1) since a solution is pushed out by a next solution, there are mixings of the solutions, resulting in forming of epitaxial layers which are different from a designed one,
(2) since the piston 6 and V-shaped bent hole 8 are provided, the apparatus becomes complicated, and the process of the method becomes troublesome, and
(3) since the V-shaped bent hole 8 is used, it is difficult to entirely remove the last solution from the surface of the substrate 1.